In cold rolling of thin metal strip, contact conditions between the work rolls and the strip are of great importance: roll deformations and their effect on strip thickness variation may lead to strip ... [more ▼]

In cold rolling of thin metal strip, contact conditions between the work rolls and the strip are of great importance: roll deformations and their effect on strip thickness variation may lead to strip flatness defects and thickness inhomogeneity. To control the process, several online measurements are usually carried out such as the rolling load, forward slip and strip tensions at each stand. Shape defects of the strip are usually evaluated after the last stand of a rolling mill thanks to a flatness measuring roll. However, none of these measurements is made within the roll bite itself due to the harsh conditions taking place in that area. This paper presents a sensor capable of monitoring roll deformations as well as roll radial stresses in situ and in real time. The sensor emits ultrasonic pulses that reflect from the roll surface. The time-of-flight (ToF) of the pulses is recorded during the testing. The sensor system was incorporated into a work roll and tested on a pilot rolling mill. Measurements were taken as steel strips were rolled under different strip elongation. Roll deformation and radial stresses obtained from the experimental data are in good agreement with numerical results computed with a cold rolling model developed in non-linear Finite Element software. [less ▲]

The manufacturing process of glass fibers used for the reinforcement of composite materials consistsin drawing a free jet of a molten glass at high temperature into fibers using a winder. This process is ... [more ▼]

The manufacturing process of glass fibers used for the reinforcement of composite materials consistsin drawing a free jet of a molten glass at high temperature into fibers using a winder. This process is sensitive to numerous disturbances that can cause the fiber to break during the drawing process, and thus reduce the process efficiency. The underlying physics of the forming of a single fiber is investigated here through numerical simulations, and results are validated with measurements obtained on a dedicated experimental unit. Both a two-dimensional axisymmetric and a simplified one-dimensional model are used to simulate the high-temperature region before glass transition. The influence of key parameters and physical mechanisms on the internal stress is investigated through a sensitivity analysis. The simplified model is then used to identify the optimal operating window and to assess the impact of temperature inhomogeneities at the bushing plate. Results show that the initial region close to the tip is critical, and that a low cooling rate reduces the stress. Operating at high tip temperature, large drawing velocity and small tip radius is then found to be the best strategy to minimize the stress. Finally, it is shown that the heat pattern of the bushing plate is one of the most important causes for disturbance in the process. [less ▲]

A recently developed AlMgSc alloy is studied since this material, which is well adapted to the aeronautic domain, is poorly known. The first objective is to reach a better knowledge of this alloy to ... [more ▼]

A recently developed AlMgSc alloy is studied since this material, which is well adapted to the aeronautic domain, is poorly known. The first objective is to reach a better knowledge of this alloy to provide the missing useful information to the aeronautic industry and to help research institutes who want to simulate sheet forming processes by Finite Element (FE) simulations. A set of experimental tests has been performed on the as-received sheets, material laws have been chosen and the corresponding material parameters have been adjusted to correctly describe the material behaviour. The second objective is to study the applicability of the Single Point Incremental Forming process (SPIF) on this material. Truncated cones with different geometries were formed and the maximum forming angle was determined. A numerical model was developed and proved to be able to predict both the force evolution during the process and the final geometrical shape. Moreover, the model helps reaching a better understanding of the process. The characterisation method described in this research and applied on the AlMgSc alloy can be extended to other alloys. In addition, the numerical simplified model, able to accurately describe the SPIF process with a reduced computation time, can be used to study more complex geometries. [less ▲]

The strain rate dependence of plastic yield and failure properties displayed by most metals affects energies, forces and forming limits involved in high speed forming processes. This paper investigates the influence of the strain rate on the forming properties of one laboratory made and three commercial steel grades: a CMnAl TRIP steel, the ferritic structural steel S235JR, the drawing steel DC04 and the ferritic stainless steel AISI 409. First, split Hopkinson tensile bar (SHTB) experiments are carried out to assess the influence of the strain rate on the materials’ stress–strain curves. Subsequently, the obtained SHTB results, together with static tensile test results, are used to model the constitutive behaviour of the investigated steels using the phenomenological Johnson–Cook (JC) model and the Voce model, thus allowing dynamic modelling of forming processes. Finally, forming limit diagrams (FLDs) are calculated using the Marciniak–Kuczynski method. The results clearly show that the effect of the strain rate on forces and energies involved in a forming process, and the forming limits is non-negligible and strongly material dependent. [less ▲]

Rapid prototyping process called Optoform shapes functional parts from a photocurable paste. This paste contains metal powder, resin, UV photoinitiator and wetting agent. After processing on the Optoform machine, a post-treatment is applied (debinding+sintering). During the post-treatment, the residual carbon coming from the resin modifies the composition of the metal and its melting point. This modification affects densification mechanisms, which leads to a residual porosity that lowers mechanical characteristics. We will present theoretical consideration leading to the optimization of the formulation. To improve the process, bimodal powder is used and thermal treatment is adapted. (c) 2007 Elsevier B.V. All rights reserved. [less ▲]

3D finite element analysis is employed to simulate a cold roll-forming process. Numerical results of longitudinal strains and displacement trajectories are compared with experimental results available in ... [more ▼]

3D finite element analysis is employed to simulate a cold roll-forming process. Numerical results of longitudinal strains and displacement trajectories are compared with experimental results available in the literature. Through a parametri study, significant impacts of the yield limit and the work-hardening exponent on the product quality are observed, whereas forming speed and friction at roll-sheet interface appear to play a minor role. (C) 2007 Elsevier B.V. All rights reserved. [less ▲]

An investigation of the rotary forging process of a 2024 aluminium rod is summarised. Some dispersion in mechanical properties and chemical composition of the base material is permitted. Samples of two ... [more ▼]

An investigation of the rotary forging process of a 2024 aluminium rod is summarised. Some dispersion in mechanical properties and chemical composition of the base material is permitted. Samples of two material batches were selected: one just stays near the upper limit of tolerance and the other has mean properties. Tensile and compression tests confirm the different mechanical behaviours and allow the identification of constitutive laws parameters. Optical metallography after T3 and T10 thermal treatments and differential thermal analysis provide the grain size and precipitation characteristics of each material batch, which explain their different mechanical behaviours. The industrial rod studied is usually forged in two operations: a first forging process, then a T10 thermal treatment followed by a second forging step. Industrial practise shows that manufacturing the rod with one forging step fails. FEM simulations of the process coupled with a fracture criterion confirm the advantage of a two-step process compared to a single forging step. [less ▲]

In this paper, the Arbitrary Lagrangian Eulerian formalism is used to compute the steady state of a 3D U-shaped cold roll forming process. Compared to the Lagrangian case, this method allows to keep a ... [more ▼]

In this paper, the Arbitrary Lagrangian Eulerian formalism is used to compute the steady state of a 3D U-shaped cold roll forming process. Compared to the Lagrangian case, this method allows to keep a refined mesh near the tools, thus allowing accurate contact prediction all along the computation with a limited number of elements. Mesh can also be kept refined in the bending zone, thus leading to accurate representation of the sheet with a limited computational time. The main problem of this kind of simulation lies in the rezoning of the nodes on the free surfaces of the sheet. A modified iterative isoparametric smoother is used to manage this geometrically complex and CPU expensive task. (c) 2006 Elsevier B.V. All rights reserved. [less ▲]

This work presents an experimental characterization of the mechanical behaviour of the EK4 deep drawing steel. The experimental procedure encompasses spectrometry, rnetalography, tension testing and ... [more ▼]

This work presents an experimental characterization of the mechanical behaviour of the EK4 deep drawing steel. The experimental procedure encompasses spectrometry, rnetalography, tension testing and hardness measurements. Special attention is devoted to the derivation of the elastic and plastic parameters involved in the assumed constitutive model based on the anisotropic Hill-48 yield criterion. The simulation of the deformation process during the whole tensile test is subsequently performed with the aim of assessing the adequateness of the proposed methodology. It should be mentioned that the material parameters obtained with this procedure are the basic data for the modelling and experimental validation of different deep drawing applications presented in Part II of this work. (c) 2005 Elsevier B.V. All rights reserved. [less ▲]

This paper presents the modelling and experimental validation of three different deep drawing applications: the Erichsen test, a cylindrical cup test and an industrial sheet metal forming process. The ... [more ▼]

This paper presents the modelling and experimental validation of three different deep drawing applications: the Erichsen test, a cylindrical cup test and an industrial sheet metal forming process. The sheet forrning material considered in the study is the EK4 steel characterized in Part I of this work. A finite element analysis of the deformation process is performed with a large strain hyperelastic shell formulation including the Hill-48 associate plasticity model. The experimental validation of the results provided by the simulation encompasses the punch force evolution together with the in-plane principal deformations and thickness distributions of the final deformed part. (c) 2005 Elsevier B.V. All rights reserved. [less ▲]

A model of cold rolling taking into account lubrication in mixed mode was developed. The main objective is to obtain a numerical tool that permits us to optimise a mill configuration from the lubrication ... [more ▼]

A model of cold rolling taking into account lubrication in mixed mode was developed. The main objective is to obtain a numerical tool that permits us to optimise a mill configuration from the lubrication point of view. It means that lubricant viscosity but also roll diameter and roughness, rolling diagrams, etc could be modified to improve stability and efficiency of the mill. A modified slab method is solved iteratively and is coupled with a sophisticated tribological model. A general calculation of the modified Reynolds equation is presented in order to evaluate the fluid pressure for any piezoviscosity law. The coupling is made through the calculation of fluid thickness and friction along the roll bite. The evolution of the cylinder/strip contact area due to the asperity crushing along the roll bite is also considered. A parametric study has been undertaken in order to determine the influence of various process parameters on friction and lubricant flow. Applications to industrial cases obtained from Cockerill Sambre plant will show the applicability of the method. (C) 2004 Elsevier B.V. All rights reserved. [less ▲]

The quality of springback prediction for a sheet metal forming process depends on a precise estimate of the elasto-plastic stress distribution throughout the metal sheet. The use of low-order conventional ... [more ▼]

The quality of springback prediction for a sheet metal forming process depends on a precise estimate of the elasto-plastic stress distribution throughout the metal sheet. The use of low-order conventional finite elements may be, without any proper treatment, responsible for low quality prediction because of volumetric and shear lockings. In this study, the enhanced assumed strain technique will be exploited for locking removal. The quality of the numerical simulation is evaluated through a comparison with other popular techniques like selective and uniform reduced integration. In contrast to the latter, and thanks to a full numerical integration scheme, the enhanced assumed strain element is very efficient in accurately capturing the development of plastic flow. This enables a reliable prediction of springback even with a rather coarse mesh. (C) 2004 Elsevier B.V. All rights reserved. [less ▲]

Nowadays, computer simulations of metal forming processes using the finite element method (FEM) have reached some level of maturity. The purpose of inverse problems is to determine the simulation input ... [more ▼]

Nowadays, computer simulations of metal forming processes using the finite element method (FEM) have reached some level of maturity. The purpose of inverse problems is to determine the simulation input data for one or more of these forming processes, leading to a desired result. The first example is called parameter identification. This consists in evaluating the material parameters for material behavior laws that would lead to the most accurate model, minimizing the difference between experimental results and the corresponding FEM simulation. The second example is initial geometry and tool shape design, consisting in determining the initial shape of the specimen and/or the shape of the forming tools, in order to provide the desired final geometry after the forming process. Both inverse problem examples can be formulated as optimization problems. In this paper, the authors propose to solve these optimization problems with different non-linear optimization methods and to compare their efficiency. (C) 2003 Elsevier Science B.V. All rights reserved. [less ▲]

This paper deals with a thermo-elasto-viscoplastic formulation for the simulation of metal forming involving large deformations. The authors present the governing equations of the model and some ... [more ▼]

This paper deals with a thermo-elasto-viscoplastic formulation for the simulation of metal forming involving large deformations. The authors present the governing equations of the model and some applications to superplastic forming. The numerical examples illustrate the potentiality of the finite-element code METAFOR based on this formulation. (C) 2003 Elsevier Science B.V. All rights reserved. [less ▲]

Although finite element analysis (FEA) is successful in simulating complex industrial sheet forming operations, the accurate and reliable application of this technique to springback has not been widely ... [more ▼]

Although finite element analysis (FEA) is successful in simulating complex industrial sheet forming operations, the accurate and reliable application of this technique to springback has not been widely demonstrated. Several physical parameters, as well as numerical, influence this phenomenon and its numerical prediction. In this paper, we investigate the impact of these parameters on the springback appearing in a 2D U-draw bending. (C) 2002 Elsevier Science B.V. All rights reserved. [less ▲]

In this paper, the lubrication problem in numerical simulation of rolling process is presented. In this case, the recent and complex model of Marsault for the solution of the mixed lubrication regime has ... [more ▼]

In this paper, the lubrication problem in numerical simulation of rolling process is presented. In this case, the recent and complex model of Marsault for the solution of the mixed lubrication regime has been implemented and tested. This model requires the use of the finite difference method to work properly. We will discuss the advantages and the difficulties encountered when trying to solve the same problem with the finite element method in a general frame. Finally, a finite element formulation for the solution of the time-dependent Reynolds' equation coupled with the deformation of the workpiece is proposed. (C) 2002 Elsevier Science B.V. All rights reserved. [less ▲]

This paper presents a constitutive law based on Taylor’s model implemented in our non-linear finite element code LAGAMINE. The yield locus is only locally described and a particular interpolation method ... [more ▼]

This paper presents a constitutive law based on Taylor’s model implemented in our non-linear finite element code LAGAMINE. The yield locus is only locally described and a particular interpolation method has been developed. This local yield locus model uses a discrete representation of the material’s texture. The interpolation method is presented and a deep-drawing application is simulated in order to show up the influence of the texture evolution during forming processes. [less ▲]

This paper deals with unified elasto-plastic and elastic-visco-plastic constitutive equations for metals submitted to large deformations. We present here a newly developed time integration algorithm which ... [more ▼]

This paper deals with unified elasto-plastic and elastic-visco-plastic constitutive equations for metals submitted to large deformations. We present here a newly developed time integration algorithm which is an extension to the visco-plastic range of the classical radial return algorithm for plasticity. The resulting implicit algorithm is both efficient and very inexpensive. This algorithm is also subsequently extended to frictional problems where it allows a generalisation of the classical Coulomb dry friction criterion to a criterion depending on the relative slip velocity such as those encountered in the hydrodynamic regime. (C) 1998 Elsevier Science S.A. All rights reserved. [less ▲]